According to the software engineering community, the acknowledgement is growing that a theory of software development is needed to integrate the currently myriad popular methodologies, some of which are based on opposing perspectives. Conceptual modeling (CM) can contribute to such a theory. CM defines fundamental concepts to create representations of reality to achieve ontologically sound software behavior that is characterized by truthfulness to reality and conceptual clarity. In this context, CM is founded on theories about the world that serve to represent a given domain. Ontologies have made their way into CM as tools in requirements analysis, implementation specification, and software architecture. This paper involves building a direct connection between reality and CM by establishing mapping between reality and modeling thinging machines (TMs). Specifically, Stoic ontology serves to define the existence of TM things and actions in reality. Such a development would benefit CM in addition to demonstrating that classical concepts in philosophy can be applied to modern fields of study. The TM model includes static and dynamic specifications. The dynamic level involves time-based events that can be mapped to reality. The problem concerns the nature of a time-less static description, which provides regions where the actions in events take place; without them, the dynamic description collapses. The Stoics came up with a brilliant move: the assumed reality to be a broader category than being. Reality is made of things that exist and things that subsist. In this case, the dynamic TM description is in existence, whereas the static, mapped portion of the dynamic description is in subsistence. We apply such ontology to a contract workflow example. The result seems to open a new avenue of CM that may enhance the theoretical foundation for software and system development.